Apparatus and method for protection against jamming attacks

Abstract

An apparatus is provided for protecting a main receiver against radio jamming attacks. The apparatus comprises an auxiliary receiver configured to monitor radio jamming signals and to detect energy characteristics thereof, wherein the energy characteristics comprises at least frequency. A frequency selective protection device is configured to, upon the auxiliary receiver detecting wireless signalling indicative of a jamming attack, selectively prevent signals at the frequencies of this wireless signalling from saturating the main receiver. A corresponding method, computer program and computer program products are also disclosed.

Description

[0001] APPARATUS AND METHOD FOR PROTECTION AGAINST JAMMING

[0002] ATTACKS

[0003] TECHNICAL FIELD

[0004] The technology disclosed herein relates generally to the field of communications systems, and in particular to a method and an apparatus for protecting a main receiver against radio jamming attacks.

[0005] BACKGROUND

[0006] In wireless cellular communication networks, for instance fifth generation (5G) networks, the network resources are shared by all user devices. The communication medium is the free space, which makes any type of wireless communication prone to interference and is a fundamental cause for performance degradation in the wireless networks. When the level of interference is high the user device may be unable to decode transmitted signals. This is a weakness that may be used in malicious ways to cause intentional interference and prevent legitimate user communication over specific wireless channels. This is known as jamming attacks.

[0007] Jamming attacks pose serious risks to public communication services since attacks can be launched to hinder these services. Several jammer devices are available on the market at a low cost, and the most sophisticated jamming attacks can be implemented at a very low cost using low-cost software-defined radio tools, and some basic programming skills. The 5G cellular network is expected to be the infrastructure for emergency services, natural disasters rescue, public safety and military communications, making jamming attacks a truly great threat.

[0008] The burden of countering such jamming activities falls on both ends of the wireless communication link: at the Base Station (BS) / Network (NW) side as well as on the user device side. A mobile device jammer or blocker is a device that deliberately transmits signals on the same radio frequencies as the mobile devices use. This disrupts the communication between the mobile device and the base station, efficiently disabling communication within the range of the jammer. Jammers can be used at essentially any location, but historically - and in legitimate use - they have been found primarily in places where silence is expected (e.g., entertainment venues) and wherein a phone call would be particularly disruptive. The jammers disrupt the operations of legitimate mobile device services, and therefore the use of such blocking devices is illegal in many jurisdictions unless having a legitimate license for it. The jammers also block access to emergency services. By injecting faked or replayed signals, the jammer aims at interrupting ongoing communication of mobile devices such as smartphones, laptops and mobile sensing robots. This may result in denial of service (DoS) attacks in wireless networks. With the entry of smart radio devices, such as universal software radio peripherals (USRPs), smart jammers can cooperatively and flexibly choose their jamming policies in order to block the mobile devices efficiently. Jammers can even induce the mobile device to enter a specific communication mode and then launch the jamming attacks accordingly.

[0009] In an effort to avoid intra- and inter cell interference for communication in licensed spectrum, scheduling and inter-BS coordination have been developed, together with strict rules and / or requirements for avoiding unintentional transmission outside an intended spectrum. Jamming sources may deliberately or unintentionally violate such rules and requirements, disrupting normal cellular NW operation. Intentional jamming will likely increase as 5G and 6G will address new critical services beyond enhanced Mobile Broadband (e-MBB) as well as the fact that many new services (e.g., Ultra Reliable Low Latency communication, URLLC) will be much more sensitive to communication disruption. Some wireless communication services requiring high communication reliability / availability will likely also occur in new industrial environments wherein new unintentional interference might occur. Hence, there will be a need for a higher level of protection in cellular networks than today, and this at multiple levels and places.

[0010] In view of the above it is clear that there is a need for efficient ways to handle such jammers and the problems caused by them.

[0011] SUMMARY

[0012] An objective of embodiments herein is to address and improve various aspects for handling jamming attacks. A particular objective is to provide an apparatus for handling any such jamming attacks. Another objective is to prevent jamming attacks from affecting receiving devices. Still another objective is to prevent a main receiver from being saturated by the jamming attacks. These objectives and others are achieved by the methods, apparatus, computer programs and computer program products according to the appended independent claims, and by the embodiments according to the dependent claims.

[0013] According to a first aspect, an apparatus is provided for protecting a main receiver against radio jamming attacks. The apparatus comprises an auxiliary receiver that is configured to monitor radio jamming signals and to detect energy characteristics thereof, wherein the energy characteristics comprises at least frequency. The apparatus further comprises a frequency selective protection device configured to, upon the auxiliary receiver detecting wireless signalling indicative of a jamming attack, selectively prevent signals at the frequencies of this wireless signalling from saturating the main receiver.

[0014] According to a second aspect, a method of protecting a main receiver against jamming attacks is provided. The method comprises monitoring radio jamming signals to detect energy characteristics thereof. The method further comprises to, upon detecting wireless signalling indicative of a jamming attack, selectively prevent this wireless signalling from saturating the main receiver.

[0015] According to a third aspect, a computer program is provided for protecting a main receiver against jamming attacks. The computer program comprises computer code which, when run on processing circuitry of a device, causes the apparatus to perform a method according to the second aspect.

[0016] According to a fourth aspect, a computer program product is provided comprising a computer program according to the third aspect, and a computer readable storage medium on which the computer program is stored.

[0017] Advantageously, these aspects enable an improved protection against jamming attacks. The method and apparatuses enable handling attacks from jammers (interference) by only excluding the jamming frequencies, while other frequencies can still be used for reception / transmission. Further, the main receiver is protected against jamming attacks and protected from being saturated. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0018] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, action, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, action, etc., unless explicitly stated otherwise. The actions of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0021] FIG. 1 illustrates schematically an environment in which aspects of the present teachings may be applied.

[0022] FIG. 2 illustrates schematically an apparatus according to embodiments.

[0023] FIG. 3 illustrates schematically an apparatus according to embodiments.

[0024] FIG. 4 illustrates schematically an apparatus according to embodiments.

[0025] FIG. 5 is a block diagram of an exemplary sub-band low sensitivity receiver according to embodiments.

[0026] FIG. 6 illustrates an example of an architecture for a main receiver.

[0027] FIG. 7 is a flowchart of various embodiments of a method.

[0028] FIG. 8 is a schematic diagram showing functional units of a device according to an embodiment.

[0029] FIG. 9 is a schematic diagram showing functional modules of a device according to an embodiment. FIG. io shows one example of a computer program product comprising computer readable means according to an embodiment.

[0030] DETAILED DESCRIPTION

[0031] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any action or feature illustrated by dashed lines should be regarded as optional.

[0032] Depending on type and power of a jamming signal, its impact may range from classical interference to fully blocking a receiver front end and even causing hardware damage to a sensitive Low-Noise Amplifier (LNA) stage. Most of today’s jamming mitigation solutions, such as frequency hopping, spread spectrum techniques, etc., are designed to start acting after jamming actually affects the communication process. Some of these solutions, e.g., Artificial Intelligence (Al)-based approaches in the baseband, involve heavy computational complexity and incur delays. The present inventors have identified a need for a more autonomous approach that can act immediately at the radio frequency (RF) front end and isolate any jamming signal before it reaches active parts of a radio receiver where it, in some cases, may damage even the sensitive internal components of a device, such as, for instance, transistors of an LNA or a down-conversion mixer, which may be sensitive to voltage stress, and resistors that maybe overheated.

[0033] Briefly, an apparatus is provided, in which an auxiliary receiver is arranged to monitor strong interfering signals. Such signals may indicate presence of jammers. The monitoring is made without affecting a main signal path, or at least without significantly affecting it. When the auxiliary receiver detects the presence of a jammer (based on the monitored signals), it may deactivate the main receiver. The main receiver is thereby protected from any strong jammer signals and made to operate only when conditions are deemed safe, and the main receiver can provide useful output. Depending, for instance, on received signal properties, the main receiver operation may also be adapted in other ways. For instance, an input signal may be attenuated in order to prevent saturation, however at the cost of reduced receiver sensitivity, or various filters maybe selected in order to reduce the jamming signal power input to the main receiver.

[0034] Briefly, an auxiliary receiver is used to monitor for strong interference / jamming. The receiver has a high input impedance and is thereby able to monitor circuit nodes for signals without significant effect on the main receiver performance. The auxiliary receiver is adapted for large signal levels and may have an attenuator first in a signal chain, before the mixer. After the mixers a set of complex filters, envelope detectors, and low pass filters maybe provided before any Analog to Digital Converters (ADCs). In other embodiments, the signal after the mixer may be anti-alias filtered and connected to the ADCs, and further signal processing (e.g., filtering and envelope detection) may then be performed in digital domain. Which option to choose may, for instance, depend on the signal bandwidth to be monitored, and the number of frequency bins. If a wide bandwidth is to be monitored and the number of frequency bins is limited, the analog filters and envelope detectors are favorable.

[0035] The output of the auxiliary receiver may be used to select which frequency bands to receive in the main receiver, by selectively connecting outputs of an RF filter bank to the main receiver. Additional delay can be introduced in the path to the main receiver to ensure that strong signals are detected and can be disconnected before they reach the input of the main receiver. The main receiver can then be protected from damage due to strong signals, in addition to avoiding saturation that could desensitize it during subsequent reception. The arrangement can then be used to avoid strong interference / jamming in the frequency domain, selectively receiving frequencies that are momentarily unaffected by jamming. The arrangement can be combined with a Butler matrix or a Rotman lens, and used at the different beam ports, to enable avoidance of jammers in the spatial domain as well as in time / frequency.

[0036] Next, the various embodiments will be described in more detail.

[0037] FIG. 1 illustrates schematically an environment in which aspects of the present teachings may be applied. In particular, Fig. 1 illustrates an exemplary communication system loo for wireless communication in which embodiments according to the present teachings may be implemented. The communication system IOO is illustrated in a highly schematical way as comprising several areas, often denoted cells 104, 106. These cells 104, 106 are provided by a base station 102. A radio access network (RAN) connects wireless communication devices 103 to their service provider(s), via wireless communication between the base station 102 closest to the wireless communication device 103. The communication system 100 further comprises antenna devices 105 by means of which a wireless communication is enabled between the wireless communication devices 103 and the base station 102. All this is well known and is therefore not described in further detail. The various embodiments according to the present teachings may be implemented in such communications system 100, and in entities thereof and / or entities therein. Examples of such entities are any type of user device for wireless communication, base station, evolved Node B (eNB) for Long Term Evolution networks, gNodeB (gNB) for 5G New RAdio networks, base-band unit, radio unit, radio head, Open RAN Distributed Unit (0-DU), and Open RAN Remote Radio Unit (0-RU). As noted in the background section, jamming sources 150 may deliberately or unintentionally violate rules and requirements and thereby disrupt legitimate cellular NW operation. Various methods and means are described in the following for protecting, for instance, communication devices 103 and network entities 105, 102 against such jamming sources 150.

[0038] FIG. 2 illustrates schematically an embodiment of an apparatus 10 for protecting wireless devices and network entities against jamming attacks. The apparatus 20 according to this set of embodiments enables frequency-selective jamming avoidance. A main receiver 7 (not necessarily part of the apparatus 10) is protected by introducing the apparatus 10 comprising an auxiliary receiver 4. Throughout the figures, the auxiliary receiver 4 is exemplified by a low sensitivity receiver (LSR) with high input impedance. The apparatus 10 is configured to enable monitoring of jamming occasions via the auxiliary receiver 4 without the main receiver 7 being involved in the monitoring. While the auxiliary receiver 4 performs this monitoring, the main receiver 7 may communicate within the NW 100, e.g., with the base station 102.

[0039] The auxiliary receiver 4 preferably has a receiver sensitivity [dBm] starting at a point just below the maximum input level of the main receiver 7. Signals within the range of the main receiver 7 can be detected by it, and there is thus no need for these signals to be received also by the auxiliary receiver 4. The auxiliary receiver 4 may thus be optimized for strong signals only and receive signals at levels that would saturate or damage the main receiver 4. An intention is to cover signal levels without leaving a gap for signal levels that are too strong for the main receiver 7 and too weak for the auxiliary receiver 4, and there should therefore preferably be some overlap of their respective input signal ranges. Hence, the auxiliary receiver 4 sensitivity should be slightly below the maximum level of the main receiver 7. The auxiliary receiver 4 may be seen as an energy detector.

[0040] The apparatus 10 further comprises an antenna 2 for signal reception. The antenna 2 may in turn comprise a Butler Matrix, which enables the apparatus 10 to determine, for instance, directions of beams. The antenna 2 is connected to the auxiliary receiver

[0041] 4 via narrow band RF (radio frequency) filter(s) 2. These narrow band filters 2 enable the separation of narrow bands of frequencies from a wider bandwidth signal, and in turn enabling a selectiveness in which frequencies are allowed to reach the main receiver 7.

[0042] The apparatus 10 further comprises control logic circuitry 6 controlling one or more switches 5 and also the main receiver 7. The control logic circuitry 6 may exchange data with the auxiliary receiver 4 and may also send control signaling to the switches

[0043] 5 for preventing relevant frequencies (i.e. , those of a jamming attack) from reaching the main receiver 7. The apparatus 10 is thereby enabled to selectively prevent signaling from reaching the main receiver 7. The control logic circuitry 6 controls the switches 5, by turning them on and turning them off, such as to allow or prevent passing of signals from the narrow RF filter(s) 3 to the main receiver 7. In embodiments wherein the auxiliary receiver 4 is combined with the butler matrix 2, the control logic circuitry 6 that is controlling the main receiver 7 and the switches 5, will be able to operate in light of spatial, time and frequency information that describes the jamming occasions.

[0044] In embodiments not comprising the butler matrix 2, the auxiliary receiver 4 is able to monitor only time and frequency information. The auxiliary receiver 4 is either operating the whole time, since jamming occasions / directions are typically not known beforehand, or it may be started just before planed traffic (reception, RX, occasions) by the main receiver 7, and not, for example, during deep sleeps.

[0045] In other scenarios, the auxiliary receiver 4 may be operating to assist other nearby receivers by, for instance, providing information about detected jamming characteristics, such as e.g., frequency-, time- and / or spatial information. The auxiliary receiver 4 should be of low power, with high input impedance. The low power is preferred in case the auxiliary receiver 4 is a standalone application, medical applications, alarm systems, .etc., and the high input impedance is preferred so that it does not affect the signal that is passed on to the main receiver 7.

[0046] The auxiliary receiver 4 may be a simple energy detection receiver or it may be designed to be a full-fledged receiver with low sensitivity. In preferable embodiments, the auxiliary receiver 4 is a wideband receiver so that it can be faster, i.e., have a shorter group delay than narrow filters have, in order to make decisions on the jamming occasions / directions.

[0047] The antenna 2 may be omnidirectional antennas in order tobe able to receive from all directions, and to ensure that jammers are detected from all directions. A round robin jamming occasion monitoring may, for instance, be used with the auxiliary receiver(s) 4 connected to different Butler matrix beam ports. As another example, one auxiliary receiver per beam port may be used and operated simultaneously. Any termination of certain identified signals with jammed frequencies is performed after the RF filters 3. Attenuators (not illustrated) may also be included; in case they are needed. As an exemplary case, if a jamming signal is sufficiently attenuated it can be processed by the main receiver 7, and additional information about the jammer may thereby be extracted. This is typically beyond the capabilities of the auxiliary receiver 4-

[0048] The functioning of the apparatus 10 is described next. In a preferred embodiment, the initial state is that the switches 5 are blocking signals to the main receiver 7. In other embodiments, the initial state is that the switches 5 are connected to the main receiver 7, and when jamming signaling is detected, the switches 5 are disconnected. Once enough jamming information has been obtained by the auxiliary receiver 4 via the antennas 2, the main receiver 7 may be connected to one or more filter output signals to start to receive communications signals, as will be described in different embodiments herein. The auxiliary receiver 4 maybe designed to be fast enough without the need for additional delays introduced in the main signal path. If a jammer is turned on abruptly in an effort to damage the main receiver 7, the auxiliary receiver 4 has to react fast enough to disconnect the main receiver 7 from the antenna signals, in particular before a large amplitude signal reaches the main receiver input. The signal passes the narrow band RF filters, which provide some delay. However, the amplitude rise time of the narrow filter output is limited. Even though the jammer would be turned on abruptly, the amplitude rises slowly at the output of the narrow-band RF filters, and it will take several nanoseconds from it starts to rise to reach full amplitude. This while the auxiliary receiver 4 reacts in only a few nanoseconds and turns off the switches, and this is hence enough to protect the main receiver 7.

[0049] The acquired jamming information may, for example, be used, for: scheduling / redundancy in time (in case a smart jammer is used) and frequency. If spatial information about the jamming signal is obtained, this may also be used in order to avoid communication in such directions and / or to assist in identifying a location of the jammer, power control, additional redundancy / coding, applying Modulation Coding Scheme (MCS) adaptation to that effect, and / or reporting the jamming information to a central entity (BS / NW).

[0050] The characteristics of the jammer can be identified in different ways by the apparatus 10, 20, 30. Frequency and time analysis are possible for embodiments wherein the apparatus 10, 20, 30 comprises narrow RF filters. Thereby the identification of the frequency bands and the periodic! ty / pattern of a modulated jamming tone is enabled. Another identification of jammer characteristics is spatial analysis; it is possible to use triangulation given the signal strength from multiple points as reported by devices and thereby identify the direction of jamming.

[0051] Another way to identify characteristics of the jammer is to use spatial analysis, performed in a single device. For instance, the auxiliary receiver 4 may combine received signals from multiple antennas’ signal paths and combine them with different combining weights and perform spatial scanning by controlling the weights. In other embodiments, different beam port signals maybe used in a Butler matrix or Rotman lens connected to the multiple antennas.

[0052] FIG. 3 illustrates schematically an apparatus 20 according to embodiments. In this set of embodiments, a frequency-selective jamming avoidance is enabled. The apparatus 20 comprises a sub-band detection and the auxiliary receiver 14 receives signals directly from the Butler matrix of the antennas 12. The auxiliary receiver 14 may be used in combination with switch(es) 15 and a delay block, shown as a narrow filter bank 13, and thereby protect the input of the main receiver 17. In particular, when the auxiliary receiver 14 detects a high signal power, then the path to the main receiver 17 may quickly be eliminated. This elimination may be achieved by the control logic circuitry 16 controlling the switches 15 such as to block the sub-bands that are found to contain jamming signals. In a more advanced setup, the filter bank 13 and multiple switches 15 are used, and the auxiliary receiver 14 is configured to monitor the antenna signal before the filter bank 13, as indicated by the arrow from the antennas 12 to the auxiliary receiver 14. The control logic circuitry 16 switches off paths to the main receiver 17 when the auxiliary receiver 14 detects sub-bands with strong interference. In case a group delay of the filters in the filter bank 13 does not sufficiently exceed the delay of the auxiliary receiver 14 including its filters, additional delays can be introduced in the signal path, in order to guarantee that the switches 15 are turned off in time to protect the main receiver 17. The delay of the auxiliary receiver can also be reduced compared to the narrow RF filters 13, by using slightly wider bandwidth and / or lower filter order. In this way the main receiver 17 can use parts of the frequency band that are not affected by the detected jamming signaling. Further, if sufficient redundance is introduced in the signal, e.g., via appropriate MCS selection, the information can be recovered, that has not been received using this time-frequency technique.

[0053] FIG. 4 illustrates schematically another embodiment of an apparatus 30 for protecting wireless devices and network entities against jamming attacks. The apparatus 30 according to this set of embodiments enables full-band spatial jamming avoidance. In line with the previous sets of embodiments, also this apparatus 30 comprises antennas 22 preferably including a butler matrix, an auxiliary receiver 24, control logic circuitry 26 and switches 25. The apparatus 30 of these embodiments differs from the embodiments described in relation to figures 2 and 3 in that it has no narrow radio frequency filters. Thus, the feature of the previous embodiment of frequency selectiveness is not available, and either all frequencies are blocked, or none is. As in the previous embodiments, the signal path to a main receiver 27 is switched off to thereby protect the main receiver 27. This set of embodiments may be provided at a lower cost compared to the earlier embodiments.

[0054] The apparatus 10, 20, 30, described in various embodiments, maybe applied both in a base station and in a user device. In various embodiments, the auxiliary receiver 4, 14, 24 only detects signals with large amplitudes, so a low noise figure is not necessary. Instead, the apparatus 10, 20, 30 can be designed to have a high input impedance in order to sense the Radio Frequency (RF) voltage in a circuit node to monitor the incoming signal without significantly affecting it. Rather than having a low noise amplifier first in the signal chain, the apparatus 10, 20, 30 may comprise a voltage attenuator, then followed by down-conversion mixers. In the baseband there could be complex analog filter-banks, followed by envelope detectors and low pass filters before ADCs, to enable wideband and low power spectrum analysis, or the ADCs could be connected after the mixers and lowpass filters, and the spectrum analysis is performed by, for instance, a Fast Fourier Transform (FFT) in the digital domain to yield a more compact solution.

[0055] FIG. 5 is a block diagram of an exemplary auxiliary receiver. The auxiliary receiver shown in figure 5 may, for instance, be used in the apparatus 20 shown and described in relation to figure 3. The auxiliary receiver 4, 14, 24 may comprise a sub-band low sensitivity receiver. In figure 5 an LSR 4, 14, 24 that monitors four simultaneous frequency bins is shown, but this is just an example and could be scaled to more or fewer bins according to need. The node or device to be monitored is connected to a tap / attenuator block 28. The tap / attenuator 28 has a high input impedance and attenuates the signal voltage that is provided to a mixer 29. The tap / attenuator 28 features passive circuit elements that are able to handle large signal voltages without being damaged or generating significant distortion. A simple example of a tap / attenuator 28 is a small series capacitance, providing voltage division with the input impedance of the mixer. The mixer 29 could be a passive mixer, since no gain is needed, and high linearity is a priority. The mixer 29 is preferably a quadrature mixer, which could be realized by driving it with a 25% duty cycle quadrature local oscillator signal.

[0056] The quadrature frequency down-converted signal at the mixer output is connected to a set of complex bandpass filters (CBPF) 40. Some of these filters 40 may be tuned to positive frequencies and others to negative, where the complex representation with quadrature signals allows distinction between positive and negative frequencies. The quadrature output signals of the complex filters are connected to detectors 41. The detectors 41 may be envelope detectors, power detectors, or square root power detectors. The detectors 41 will use all the quadrature phases to reduce the ripple of the output, which may still need some low pass filtering to reduce the ripple, before feeding it to analog-to-digital converters (ADCs) 44.

[0057] The ADCs 44 will provide measures of the signal level in each frequency bin. Using these levels, decisions can be taken on whether or not to include the different frequency bins to the main receiver 7, 17, 27. The ADCs 44 may have rather few levels, i.e., a few bits is sufficient, to support those decisions.

[0058] When a signal with a level that can damage the main receiver 7, 17, 27 is present, it is important to detect that quickly. For this purpose, a separate comparator 42 maybe used prior to low pass filtering 43 the detected signal. This is illustrated for one of the branches in figure 5 but may, in various embodiments, be present in several or all branches. The information that there is a risk for damage can be obtained faster, by eliminating the delay of the low pass filter 43. When the signal is so large that there is risk for damage, it can be decided to block signaling from reaching the main receiver 7, 17, 27, without waiting for the more accurate value which the low pass filter provides. The output of the comparator 42 may be used to clock a D flip-flop to store the detection until it is reset. Another option is to also bypass the detector 41, placing comparators 42 at all four quadrature phases directly at the complex filter 40 output, to monitor if any signal phase amplitude exceeds a set threshold, and then clock a flip-flop to store that the event occurred.

[0059] An alternative architecture to the one shown in figure 5 is to digitize the mixer 29 output directly after wideband low pass filtering. This will move the signal processing to the digital domain and provide more flexibility in terms of number of frequency bins. However, if the bandwidth to analyze is wide, the power consumption may be significantly higher than for the architecture in figure 5.

[0060] FIG. 6 illustrates an example of an architecture for a main receiver 7, 17, 27, illustrated together with the narrow filters 13 and switches 15. An RF filter bank 3, 13 has a single input (e.g., receiving signaling from an antenna) and multiple outputs. At each output there is a switch 5, 15 that can be used to select if the main receiver 7, 17, 27 should be connected to that output or not. After the switch 5, 15, the main receiver signal chain begins, with a low noise amplifier (LNA) 62, followed by a quadrature mixer 63. In order to further improve the selectivity between different frequency bands there may then be a complex bandpass filter 64. This can be selectively activated when needed, i.e., when strong interference or jamming is present in some frequency bands.

[0061] After the complex bandpass filters 64 the signals from the different branches are combined, for instance by merging current mode signals. Then the signals (I and Q) are input to low pass filters (LPFs) 65, amplified in a variable gain amplifier (VGA) 66 and converted to digital form in an ADC 67. The low pass filter 65 may be reconfigurable dependent on whether the CBPFs 64 are active or not. In case the CBPFs 64 are active, the selectivity of the LPF 65 can be reduced, e.g., by reducing the filter order.

[0062] Next, some particular exemplary use cases are given. The signal levels received due to a jamming device can be very strong, for instance if the jammer gets close, has high- gain directional antennas aimed towards the victim receiver, and has high transmit power. In extreme cases the jammer can even cause damage to victim receivers. Some example numbers are given here to provide some understanding about the signal levels.

[0063] Assume operation at 3GHz, and that the jammer transmitter has an output power of 100W. Two different types of jammers are used in this example, one with lodB antenna gain, and one with 3odB, corresponding to a im diameter parabolic antenna.

[0064] At 100m line-of-sight distance from the jammer the power received by a receive antenna element with sdBi gain becomes 3dBm for the high gain jammer, and - lydBm for the low gain jammer. 3dBm corresponds to a voltage with a peak amplitude of 0.45V in a typical 5oOhm antenna impedance, which should not cause permanent damage, but may approach the limit.

[0065] At 10m line-of-sight distance the received power is 2odB stronger, equal to 23dBm for the high gain jammer and 3dBm for the low gain. Here the jammer could clearly cause damage, with 23dBm corresponding to 4.5 Volt peak in 50 Ohms, by far exceeding the gate breakdown voltage of typical transistors used in low noise amplifiers.

[0066] At im distance the low gain jammer will also cause 23dBm received power, and cause damage.

[0067] As can be seen in extreme cases, the jammer maybe strong enough to cause damage, but in a more typical scenario the signal level will be a bit less, at about -2odBm to odBm. The jammer is then located at some distance, say 100m in the example above and with antenna gain between lodB and 3odB as above. While the receiver will not break from such signal levels, it will be heavily compressed and will be unable to receive the weak signals often required for communication.

[0068] It is thus advantageous to have a separate receiver that can detect strong signals, and that can be used to steer the communication receiver away from strong signals that would cause saturation or even damage to it. As the strong signals are detected by a receiver that do not need to handle weak signals, the power consumption of the auxiliary receiver can be limited.

[0069] Assume the auxiliary receiver should handle signal levels between +25dBm and - 2odBm. As +25dBm corresponds to 5.6V peak over 50 Ohms, we start by a voltage attenuator of 20 times, bringing the signal down to 0.28V peak. After conversion loss in the mixers, we will have about 0.2V peak into the filters in figure 4, which will be possible to handle with different filter architectures. For the signal level of -2odBm input, we get 45dB less signal than at +25dB in, i.e., imV peak at the filter input. If the input referred noise of the filter is 50nV / sqrt(Hz) and the bandwidth is 10MHz, we get o.i6mV rms input referred noise in total, corresponding to a i3dB SNR, which should be enough to detect the presence of the jammer. It is thus feasible to provide an auxiliary receiver that can detect signals from -2odBm to +25dBm. The main receiver then has the responsibility for handling signals below -2odBm, for which sufficient linearity, selectivity, phase noise performance, etc. is needed. These signals could include both signals that one wish to receive, as well as regular interference and jammers. By limiting the level to handle to

[0070] -2odBm using the auxiliary receiver 4, 14, 24 presented herein in various embodiments, significant power can be saved in the analog part of the main receiver 7, 17, 27.

[0071] FIG. 7 is a flowchart of various embodiments of a method. The method 50 is highly valuable for protecting a main receiver 7, 17, 27 against jamming attacks. The method 50 is performed in the apparatus 10, 20, 30 described in various embodiments.

[0072] The method 50 comprises monitoring 52 radio jamming signals in order to detect energy characteristics thereof. This monitoring for radio jamming signals can be performed simultaneously as the main receiver 7, 17, 27 communicates in an access network 100, as the monitoring 52 is performed by an auxiliary receiver 4, 14, 24.

[0073] Upon detecting 54 wireless signalling that is indicative of a jamming attack, the method 50 selectively prevents the wireless signalling from saturating the main receiver 7, 17, 27.

[0074] In an embodiment, the method 50 comprises preventing the wireless signalling from reaching the main receiver 7, 17, 27 by control logic circuitry 6, 16, 26 switching off one or more switches 5, 15, 25 that are arranged in a signal path to the main receiver 7, 17, 27. This efficiently prevents the undesired wireless signalling from harming the main receiver 7, 17, 27.

[0075] In another embodiment, the method 50 comprises delaying the received signals in one or more narrow-band filters to thereby prevent the received jamming signals from reaching the main receiver 7, 17, 26. In a variation of this embodiment, the one or more switches in a signal path to the main receiver 7, 17, 26 are switched off, before the delayed received jamming signals reach the main receiver 7, 17, 26.

[0076] In various embodiments, the method 50 blocks the wireless signalling indicative of a jamming attack during specified time intervals. While this jamming attack is prevented, the main receiver is still able to selectively receive frequencies that are unaffected by the jamming. In still other embodiments, the method 50 uses the knowledge on jamming signals, as determined by the auxiliary receiver 4, 14, 24, to determine, for instance, in which direction to communicate, when to communicate and at which frequency / frequencies to communicate.

[0077] In various embodiments, the method 50 comprises passing, in the frequency selective protection device 6, 16, 26 one or more frequency sub-bands to the main receiver 7, 17, 27 and blocking any frequency sub-band exceeding a set power threshold.

[0078] The method 50, as described in various embodiments, provides a number of advantages. The method provides an improved protection against jamming attacks by excluding only the jamming frequencies. The main receiver is protected from jammer s / interference since affected frequency regions being excluded, while reception is still possible in the unaffected frequencies. The main receiver is thereby protected against jamming attacks and damage that could otherwise result.

[0079] Further, the auxiliary receiver has preferably a high input impedance and has only a minor effect on the main receiver performance in the absence of jammers. Still further, the auxiliary receiver may have low power, low cost, and monitor wide bandwidth, thus keeping the costs at a minimum.

[0080] Fig. 8 schematically illustrates, in terms of a number of functional units, the components of an apparatus 10, 20, 30 according to an embodiment. Processing circuitry no is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 330 (for instance as shown in Fig. 10), e.g., in the form of a storage medium 130. The processing circuitry no may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0081] Particularly, the processing circuitry 110 is configured to cause the apparatus 10, 20, 30 to perform a set of operations, or actions, as disclosed herein. For example, the storage medium 130 may store the set of operations, and the processing circuitry 110 maybe configured to retrieve the set of operations from the storage medium 130 to cause the apparatus 10, 20, 30 to perform the set of operations. The set of operations may be provided as a set of executable instructions. The processing circuitry no is thereby arranged to execute the method as herein disclosed in various embodiments.

[0082] The storage medium 130 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0083] The apparatus 10, 20, 30 may further comprise a communications interface 120 (shown by dashed lines for indicating that it is optional) for communications with other entities, functions, nodes, and devices, over suitable interfaces. As such the communications interface 120 may comprise one or more transmitters and receivers, comprising analogue and digital components.

[0084] The processing circuitry no controls the general operation of the apparatus 10, 20, 30 e.g., by sending data and control signals to the communications interface 120 and the storage medium 130, by receiving data and reports from the communications interface 120, and by retrieving data and instructions from the storage medium 130. Other components, as well as the related functionality, of the apparatus 10, 20, 30 are omitted in order not to obscure the concepts presented herein.

[0085] Fig. 9 schematically illustrates, in terms of functional modules, the components of an apparatus 10, 20, 30 according to an embodiment. The apparatus 10, 20, 30 of Fig. 9 comprises a number of functional modules; a monitor module 210 configured to monitor radio jamming signals and to detect energy characteristics thereof, and a prevent module 220 configured to selectively prevent signals from saturating a main receiver. The apparatus 10, 20, 30 of Fig. 9 may further comprise optional functional modules, such as a delay module configured to delay frequencies of the signalling in one or more narrow-band filters. In general terms, each functional module 210 - 230 may be implemented in hardware or in a combination of hardware and software. Preferably, one or more or all functional modules 210 - 230 maybe implemented by the processing circuitry no, possibly in cooperation with the communications interface 120 and the storage medium 130. The processing circuitry 110 may thus be arranged to fetch, from the storage medium 130, instructions as provided by a functional module 210 - 230 and to execute these instructions, thereby performing any actions of the apparatus 10, 20, 30 as disclosed herein. Fig. io shows one example of a computer program product 330 comprising computer readable means 340. On this computer readable means 340, a computer program 320 can be stored, which computer program 320 can cause the processing circuitry no and thereto operatively coupled entities and devices, such as the communications interface 120 and the storage medium 130, to execute methods according to embodiments described herein. The computer program 320 and / or computer program product 330 may thus provide means for performing any actions of the apparatus 10, 20, 30 as herein disclosed.

[0086] In the example of Fig. 10, the computer program product 330 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 330 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 320 is here schematically shown as a track on the depicted optical disk, the computer program 320 can be stored in any way which is suitable for the computer program product 330.

[0087] The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. An apparatus (io, 20, 30) for protecting a main receiver (7, 17, 27) against radio jamming attacks, the apparatus (10, 20, 30) comprising:- an auxiliary receiver (4, 14, 24) configured to monitor radio jamming signals and to detect energy characteristics thereof, the energy characteristics comprising at least frequency, and- a frequency selective protection device (6, 16, 26) configured to, upon the auxiliary receiver (4, 14, 24) detecting wireless signalling indicative of a jamming attack, selectively prevent signals at the frequencies of this wireless signalling from saturating the main receiver (7, 17, 27).

2. The apparatus (10, 20, 30) as claimed in claim 1, wherein the frequency selective protection device (6, 16, 26) comprises one or more switches (5, 15, 25) and wherein the frequency selective protection device (6, 16, 26) is configured to selectively prevent signals from saturating the main receiver (7, 17, 27) by being configured to:- switch one or more switches (5, 15, 25) in a signal path to the main receiver (7, 17, 27) upon the auxiliary receiver (4, 14, 24) detecting the wireless signalling indicative of the jamming attack.

3. The apparatus (10, 20, 30) as claimed in claim 2, wherein the switching comprises one or both of: switching off series switches, and switching on shunt switches.

4. The apparatus (10, 20, 30) as claimed in claim 2 or 3, wherein the frequency selective protection device (6, 16, 26) is configured to:- delay the frequencies of the wireless signalling indicative of a jamming attack in one or more narrow-band filters (3, 13) to selectively delay the wireless signalling, such as to ensure timely execution of the switches (5, 15, 25).

5. The apparatus (10, 20, 30) as claimed any of the preceding claims, wherein the auxiliary receiver (4, 14, 24) is a low sensitivity receiver with high input impedance.

6. The apparatus (10, 20, 30) as claimed any of the preceding claims, wherein the auxiliary receiver (4, 14, 24) and the frequency selective protection device (6, 16, 26) are configured to allow monitoring of the radio jamming signals by theauxiliary receiver (4, 14, 24) simultaneously as communicating in an access network (100) by the main receiver (7, 17, 27).

7. The apparatus (10, 20, 30) as claimed in any of the previous claims, wherein the auxiliary receiver (4, 14, 24) is configured with a sensitivity range starting below a maximum level of the main receiver (7, 17, 26).

8. The apparatus (10, 20, 30) as claimed in any of the preceding claims, wherein the auxiliary receiver (4, 14, 24) comprises bandpass filters for identifying frequency bands and timing of the received wireless signalling indicative of a jamming attack.

9. The apparatus (10, 20, 30) as claimed in any of the preceding claims, wherein the auxiliary receiver (4, 14, 24) is configured to receive signals from two or more antenna signal paths and to combine the signals with different weights, and wherein- the frequency selective protection device (6, 16, 26) is configured to control the weights for performing spatial beamforming.

10. The apparatus (10, 20, 30) as claimed in any of the preceding claims, wherein the frequency selective protection device (6, 16, 26) is configured to block the wireless signalling indicative of a jamming attack during specified time intervals in time domain.

11. The apparatus (10, 20, 30) as claimed in any of the preceding claims, wherein the main receiver (7, 17, 27) is configured to use the radio jamming signals determined by the auxiliary receiver (4, 14, 24) for determining when to communicate.

12. The apparatus (10, 20, 30) as claimed in any of the preceding claims, wherein the frequency selective protection device (6, 16, 26) is configured to pass one or more frequency sub-bands to the main receiver (7, 17, 27) and to block any frequency sub-band exceeding a set power threshold.

13. A node (102) of an access network for wireless communication, the node (102) comprising the apparatus (10, 20, 30) as claimed in any of the preceding claims.

14. A communication device (103) for wireless communication, the communication device (103) comprising the apparatus (10, 20, 30) as claimed in any of claims 1 - 12.

15. A method (50) of protecting a main receiver (7, 17, 27) against jamming attacks, the method (50) comprising:- monitoring (52) radio jamming signals to detect energy characteristics thereof, and- upon detecting (54) wireless signalling indicative of a jamming attack, selectively preventing this wireless signalling from saturating the main receiver (7, 17, 27).

16. The method (50) as claimed in claim 15, comprising preventing the wireless signalling from reaching the main receiver (7, 17, 27) by control logic circuitry (6, 16, 26) switching off one or more switches (5, 15, 25) in a signal path to the main receiver (7, 17, 27).

17. The method (50) as claimed in claim 15, comprising delaying the received signals in one or more narrow-band filters to prevent the received signals from reaching the main receiver (7, 17, 26).

18. The method (50) as claimed in claim 17, comprising turning off one or more switches in a signal path to the main receiver (7, 17, 26), before the delayed received signals reach the main receiver (7, 17, 26).

19. The method (50) as claimed any of claims 15 - 18, monitoring the radio jamming signals simultaneously as communicating in an access network (100) by the main receiver (7, 17, 27).

20. The method (50) as claimed any of claims 15 - 19, the method (50) comprises blocking the wireless signalling indicative of a jamming attack during specified time intervals.

21. The method (50) as claimed in claim 20, comprising determining, based on the jamming signals determined by the auxiliary receiver (4, 14, 24), one or more of: in which direction to communicate, when to communicate and at which frequency to communicate.

22. The method (50) as claimed in any of claims 15 - 21, comprising passing, in the frequency selective protection device (6, 16, 26) one or more frequency sub-bands to the main receiver (7, 17, 27) and blocking any frequency sub-band exceeding a set power threshold.

23. A computer program (320) for protecting an apparatus (10, 20, 30) against jamming attacks, the computer program (320) comprising computer program code, which, when executed in at least one processor of the apparatus (10, 20, 30) causes the apparatus (10, 20, 30) to perform the method (50) according to any of claims 15 - 22.

24. A computer program product (330) comprising a computer program (320) as claimed in claim 23 and a computer readable means on which the computer program (320) is stored.

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